Match point No 5 was then saved in stunning fashion by Sandgren, but it was sixth time's a charm for Chung, who continues his bid to become the first Korean Grand Slam champion. Putting up a ideal combination of baseline and net play, Federer beat Berdych 7-1 in the tiebreak to take the first set.

Federer's win against Marton Fucsovics in the fourth round was only the second time he faced a Hungarian player in 72 main draw appearances at a major.

When he didn't, Federer, who has the reputation of seeing better than the hawkeye, challenged the point. Are you okay with it?

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Berdych was presented with the first break-point opportunity of the second set when Federer netted another backhand, but the world No.2 got himself out of trouble and combined great defence with classy groundstrokes to go a break up at 5-3. "That's a good thing", Federer said.

"I was just frustrated and a bit antsy".

It is seldom that you would find Roger Federer losing his cool on the tennis court since the Swiss is generally pretty reserved with his expressions on court.

Federer said: "I think next year when we'll have 16 seeds, it's going to be quite different".

"That's why I was under pressure".

The win set Kerber up with a clash against American Keys, a semi-finalist in 2015 who has found a new lease of life under the guidance of former great Lindsay Davenport.

A dejected Berdych took little consolation from his admirable fighting effort.

"To beat him here is one of the tough things to do in our sport, I believe. That's not what happened today".

Federer got the early mini-break, and as the winners flowed from his racquet, he raced away to win the breaker 7-1 to take the set after one hour of play.

Federer was struck down with back trouble past year when he lost to Alexander Zverev in the final of the Montreal Masters and subsequently withdrew from the Cincinnati Masters.

This match nearly feels like a step down though, even if the form of the Hungarian has been good and the only question surrounding Federer is whether he will still be as dominant in the later rounds when he begins to take on higher ranked player. "May be because I stole the first set from him, he felt dejected", Federer joked.